Technical Field
The present invention relates to power systems and, more particularly, to a two-level predictive based reactive power coordination and voltage restoration system for microgrids.
Description of the Related Art
The intermittent and non-dispatchable nature of most renewable sources such as photovoltaic (PV) and wind brings new challenges to operation and control of a microgrid. For example, large amounts of PV integration may cause voltage rise issues due to reverse power flow when PV generation exceeds load demand. Additionally, wind and PV are usually operated in maximum power point tracking (MPPT) mode to achieve maximum power generation. However, availability of maximum power can be influenced by, e.g., weather conditions. Abrupt weather condition changes may cause severe voltage variations or even a voltage collapse. The voltage variation issue is more severe in islanded microgrids since no reactive power support can be obtained from the main grid. Thus, voltage control becomes a significant issue for secure operation of microgrids, especially in islanded microgrids.
The basic idea behind voltage control is reactive power compensation. Traditionally, fossil-fuel generators such as diesel generators with direct AC connections are used as the main source to provide reactive power support since it is more reliable. However, with more and more diesel generation being replaced by renewable generation, it may be insufficient at some point in time. When demand is high, it needs a large amount of active power output from diesel generation, thus limiting the available reactive power. Besides, the use of diesel generator involves high emission and high fuel cost.